Comparative whole transcriptome analysis of gene expression in three canine soft tissue sarcoma types

Soft tissue sarcomas are pleiotropic tumors of mesenchymal cell origin. These tumors are rare in humans but common in veterinary practice, where they comprise up to 15% of canine skin and subcutaneous cancers. Because they present similar morphologies, primary sites, and growth characteristics, they are treated similarly, generally by surgical resection followed by radiation therapy. Previous studies have examined a variety of genetic changes as potential drivers of tumorigenesis and progression in soft tissue sarcomas as well as their use as markers for soft tissue sarcoma subtypes. However, few studies employing next generation sequencing approaches have been published. Here, we have examined gene expression patterns in canine soft tissue sarcomas using RNA-seq analysis of samples obtained from archived formalin-fixed and paraffin-embedded tumors. We provide a computational framework for using resulting data to categorize tumors, perform cross species comparisons and identify genetic changes associated with tumorigenesis. Functional overrepresentation analysis of differentially expressed genes further implicate both common and tumor-type specific transcription factors as potential mediators of tumorigenesis and aggression. Implications for tumor-type specific therapies are discussed. Our results illustrate the potential utility of this approach for the discovery of new therapeutic approaches to the management of canine soft tissue sarcomas and support the view that both common and tumor-type specific mechanisms drive the development of these tumors.

Two distinct Sertoli cell states are regulated via germ cell crosstalk

Sertoli cells are a critical component of the testis environment for their role in maintaining seminiferous tubule structure, establishing the blood-testis barrier, and nourishing maturing germ cells in a specialized niche. This study sought to uncover how Sertoli cells are regulated in the testis environment via germ cell crosstalk in the mouse. We found two major clusters of Sertoli cells as defined by their transcriptomes in Stages VII-VIII of the seminiferous epithelium and a cluster for all other stages. Additionally, we examined transcriptomes of germ cell-deficient testes and found that these existed in a state independent of either of the germ cell-sufficient clusters. Together, we highlight two main transcriptional states of Sertoli cells in an unperturbed testis environment, and a germ cell-deficient environment does not allow normal Sertoli cell transcriptome cycling and results in a state unique from either of those seen in Sertoli cells from a germ cell-sufficient environment.

STRA8 induces transcriptional changes in germ cells during spermatogonial development

Spermatogonial development is a key process during spermatogenesis to prepare germ cells to enter meiosis. While the initial point of spermatogonial differentiation is well‐characterized, the development of spermatogonia from the onset of differentiation to the point of meiotic entry has not been well defined. Further, STRA8 is highly induced at the onset of spermatogonial development but its function in spermatogonia has not been defined. To better understand how STRA8 impacts spermatogonia, we performed RNA‐sequencing in both wild‐type and STRA8 knockout mice at multiple timepoints during retinoic acid (RA)‐stimulated spermatogonial development. As expected, in spermatogonia from wild‐type mice we found that steady‐state levels of many transcripts that define undifferentiated progenitor cells were decreased while transcripts that define the differentiating spermatogonia were increased as a result of the actions of RA. However, the spermatogonia from STRA8 knockout mice displayed a muted RA response such that there were more transcripts typical of undifferentiated cells and fewer transcripts typical of differentiating cells following RA action. While spermatogonia from STRA8 knockout mice can ultimately form spermatocytes that fail to complete meiosis, it appears that the defect likely begins as a result of altered messenger RNA levels during spermatogonial differentiation.

Focusing super resolution on the cytoskeleton

Super resolution imaging is becoming an increasingly important tool in the arsenal of methods available to cell biologists. In recognition of its potential, the Nobel Prize for chemistry was awarded to three investigators involved in the development of super resolution imaging methods in 2014. The availability of commercial instruments for super resolution imaging has further spurred the development of new methods and reagents designed to take advantage of super resolution techniques. Super resolution offers the advantages traditionally associated with light microscopy, including the use of gentle fixation and specimen preparation methods, the ability to visualize multiple elements within a single specimen, and the potential to visualize dynamic changes in living specimens over time. However, imaging of living cells over time is difficult and super resolution imaging is computationally demanding. In this review, we discuss the advantages/disadvantages of different super resolution systems for imaging fixed live specimens, with particular regard to cytoskeleton structures.

Abnormal retinal development in Cloche mutant zebrafish

BACKGROUND

Functions for the early embryonic vasculature in regulating development of central nervous system tissues, such as the retina, have been suggested by in vitro studies and by in vivo manipulations that caused additional ocular vessels to develop. Here, we use an avascular zebrafish embryo, cloche-/- (clo-/-), to begin to identify necessary developmental functions of the ocular vasculature in regulating development and patterning of the neural retina, in vivo. These studies are possible in zebrafish embryos, which do not yet rely upon the vasculature for tissue oxygenation.

RESULTS

clo-/- embryos lacked early ocular vasculature and were microphthalmic, with reduced retinal cell proliferation and cell survival. Retinas of clo mutants were disorganized, with irregular synaptic layers, mispatterned expression domains of retinal transcription factors, morphologically abnormal Müller glia, reduced differentiation of specific retinal cell types, and sporadically distributed cone photoreceptors. Blockade of p53-mediated cell death did not completely rescue this phenotype and revealed ectopic cones in the inner nuclear layer. clo-/- embryos did not upregulate a molecular marker for hypoxia.

CONCLUSIONS

The disorganized retinal phenotype of clo-/- embryos is consistent with a neural and glial developmental patterning role for the early ocular vasculature that is independent of its eventual function in gas exchange.

In vivo orientation of single myosin lever arms in zebrafish skeletal muscle

Cardiac and skeletal myosin assembled in the muscle lattice power contraction by transducing ATP free energy into the mechanical work of moving actin. Myosin catalytic/lever-arm domains comprise the transduction/mechanical coupling machinery that move actin by lever-arm rotation. In vivo, myosin is crowded and constrained by the fiber lattice as side chains are mutated and otherwise modified under normal, diseased, or aging conditions that collectively define the native myosin environment. Single-myosin detection uniquely defines bottom-up characterization of myosin functionality. The marriage of in vivo and single-myosin detection to study zebrafish embryo models of human muscle disease is a multiscaled technology that allows one-to-one registration of a selected myosin molecular alteration with muscle filament-sarcomere-cell-fiber-tissue-organ- and organism level phenotypes. In vivo single-myosin lever-arm orientation was observed at superresolution using a photoactivatable-green-fluorescent-protein (PAGFP)-tagged myosin light chain expressed in zebrafish skeletal muscle. By simultaneous observation of multiphoton excitation fluorescence emission and second harmonic generation from myosin, we demonstrated tag specificity for the lever arm. Single-molecule detection used highly inclined parallel beam illumination and was verified by quantized photoactivation and photobleaching. Single-molecule emission patterns from relaxed muscle in vivo provided extensive superresolved dipole orientation constraints that were modeled using docking scenarios generated for the myosin (S1) and GFP crystal structures. The dipole orientation data provided sufficient constraints to estimate S1/GFP coordination. The S1/GFP coordination in vivo is rigid and the lever-arm orientation distribution is well-ordered in relaxed muscle. For comparison, single myosins in relaxed permeabilized porcine papillary muscle fibers indicated slightly differently oriented lever arms and rigid S1/GFP coordination. Lever arms in both muscles indicated one preferred spherical polar orientation and widely distributed azimuthal orientations relative to the fiber symmetry axis. Cardiac myosin is more radially displaced from the fiber axis. Probe rigidity implies the PAGFP tag reliably indicates cross-bridge orientation in situ and in vivo.

Invasion of epithelial cells by Campylobacter jejuni is independent of caveolae

Caveolae are 25–100 nm flask-like membrane structures enriched in cholesterol and glycosphingolipids. Researchers have proposed that Campylobacter jejuni require caveolae for cell invasion based on the finding that treatment of cells with the cholesterol-depleting compounds filipin III or methyl-β-cyclodextrin (MβCD) block bacterial internalization in a dose-dependent manner. The purpose of this study was to determine the role of caveolae and caveolin-1, a principal component of caveolae, in C. jejuni internalization. Consistent with previous work, we found that the treatment of HeLa cells with MβCD inhibited C. jejuni internalization. However, we also found that the treatment of HeLa cells with caveolin-1 siRNA, which resulted in greater than a 90% knockdown in caveolin-1 protein levels, had no effect on C. jejuni internalization. Based on this observation we performed a series of experiments that demonstrate that MβCD acts broadly, disrupting host cell lipid rafts and C. jejuni-induced cell signaling. More specifically, we found that MβCD inhibits the cellular events necessary for C. jejuni internalization, including membrane ruffling and Rac1 GTPase activation. We also demonstrate that MβCD disrupted the association of the β₁ integrin and EGF receptor, which are required for the maximal invasion of epithelial cells. In agreement with these findings, C. jejuni were able to invade human Caco-2 cells, which are devoid of caveolae, at a level equal to that of HeLa cells. Taken together, the results of our study demonstrate that C. jejuni internalization occurs in a caveolae-independent manner.

Eye-specific gene expression following embryonic ethanol exposure in zebrafish: roles for heat shock factor 1

The mechanisms through which ethanol exposure results in developmental defects remain unclear. We used the zebrafish model to elucidate eye-specific mechanisms that underlie ethanol-mediated microphthalmia (reduced eye size), through time-series microarray analysis of gene expression within eyes of embryos exposed to 1.5% ethanol. 62 genes were differentially expressed (DE) in ethanol-treated as compared to control eyes sampled during retinal neurogenesis (24-48 h post-fertilization). The EDGE (extraction of differential gene expression) algorithm identified >3000 genes DE over developmental time in ethanol-exposed eyes as compared to controls. The DE lists included several genes indicating a mis-regulated cellular stress response due to ethanol exposure. Combined treatment with sub-threshold levels of ethanol and a morpholino targeting heat shock factor 1 mRNA resulted in microphthalmia, suggesting convergent molecular pathways. Thermal preconditioning partially prevented ethanol-mediated microphthalmia while maintaining Hsf-1 expression. These data suggest roles for reduced Hsf-1 in mediating microphthalmic effects of embryonic ethanol exposure.

Small heat shock protein HSPB1 regulates growth of embryonic zebrafish craniofacial muscles

The small heat shock protein HspB1 (Hsp27) is abundantly expressed in embryonic muscle tissues of a wide variety of vertebrate species. However, the functional significance of this expression pattern is not well established. In the present study, we observed specific, high level expression of HspB1 protein and an HspB1 gene reporter in developing craniofacial muscles of the zebrafish, Danio rerio, and examined the consequences of reducing HspB1 expression to the development and growth of these muscles. Quantitative morphometric analyses revealed a reduction in the cross-sectional area of myofibers in embryos expressing reduced HspB1 levels by as much as 47% compared to controls. In contrast, we detected no differences in the number of myofibrils or associated nuclei, nor the number, size or development of chondrocytes in surrounding tissues. We also did not detect changes to the overall organization of sarcomeres or myofibrils in embryos expressing reduced levels of HspB1. Together our results reveal a critical role for HspB1 in the growth of myofibrils and provide new insight into the mechanism underlying its developmental function.

HSF1 is essential for the resistance of zebrafish eye and brain tissues to hypoxia/reperfusion injury

Ischemia and subsequent reperfusion (IR) produces injury to brain, eye and other tissues, contributing to the progression of important clinical pathologies. The response of cells to IR involves activation of several signaling pathways including those activating hypoxia and heat shock responsive transcription factors. However, specific roles of these responses in limiting cell damage and preventing cell death after IR have not been fully elucidated. Here, we have examined the role of heat shock factor 1 (HSF1) in the response of zebrafish embryos to hypoxia and subsequent return to normoxic conditions (HR) as a model for IR. Heat shock preconditioning elevated heat shock protein expression and protected zebrafish embryo eye and brain tissues against HR-induced apoptosis. These effects were inhibited by translational suppression of HSF1 expression. Reduced expression of HSF1 also increased cell death in brain and eye tissues of embryos subjected to hypoxia and reperfusion without prior heat shock. Surprisingly, reduced expression of HSF1 had only a modest effect on hypoxia-induced expression of Hsp70 and no effect on hypoxia-induced expression of Hsp27. These results establish the zebrafish embryo as a model for the study of ischemic injury in the brain and eye and reveal a critical role for HSF1 in the response of these tissues to HR. Our results also uncouple the role of HSF1 expression from that of Hsp27, a well characterized heat shock protein considered essential for cell survival after hypoxia. Alternative roles for HSF1 are considered.

Luteinizing hormone receptor-stimulated progesterone production by preovulatory granulosa cells requires protein kinase A-dependent activation/dephosphorylation of the actin dynamizing protein cofilin

Activation of the LH receptor (LHR) on preovulatory granulosa cells stimulates the cAMP/protein kinase A (PKA) pathway to regulate expression of genes required for ovulation and luteinization. LHR signaling also initiates rearrangement of the actin cytoskeleton. Because disruption of the actin cytoskeleton has been causally linked to steroidogenesis in various cell models, we sought to identify the cellular mechanisms that may modulate reorganization of the actin cytoskeleton and to determine whether cytoskeletal reorganization is required for steroidogenesis. Herein we report that LHR signaling in preovulatory granulosa cells promotes rapid dephosphorylation of the actin-depolymerizing factor cofilin at Ser3 that is dependent on PKA. The LHR-stimulated dephosphorylation of cofilin(Ser3) switches on cofilin activity to bind actin filaments and enhance their dynamics. Basal phosphorylation of cofilin(Ser3) is mediated by active/GTP-bound Rho and downstream protein kinases; LHR signaling promotes a decrease in active/GTP-bound Rho by a PKA-dependent mechanism. LHR-dependent Rho inactivation and subsequent activation of cofilin does not involve ERK, epidermal growth factor receptor, or phosphatidylinositol 3-kinase pathways downstream of PKA. To understand the biological significance of cofilin activation, preovulatory granulosa cells were transduced with a mutant cofilin adenoviral vector in which Ser3 was mutated to Glu (S-E cofilin). Inactive S-E cofilin abolished LHR-mediated reorganization of the actin cytoskeleton and caused a 70% decrease in LHR-stimulated progesterone that is obligatory for ovulation. Taken together, these results show that LHR signaling via PKA activates a cofilin-regulated rearrangement of the actin cytoskeleton and that active cofilin is required to initiate progesterone secretion by preovulatory granulosa cells.

Molecular interactions between T cells and fibroblast-like synoviocytes: role of membrane tumor necrosis factor-alpha on cytokine-activated T cells

The mechanism of fibroblast-like synoviocyte (FLS) transformation into an inflammatory phenotype in rheumatoid arthritis (RA) is not fully understood. FLS interactions with invading leukocytes, particularly T cells, are thought to be a critical component of this pathological process. Resting T cells and T cells activated through the T-cell receptor have previously been shown to induce inflammatory cytokine production by FLS. More recently, a distinct population of T cells has been identified in RA synovium that phenotypically resembles cytokine-activated T (Tck) cells. Using time lapse microscopy, the interactions of resting, superantigen-activated, and cytokine-activated T cells with FLS were visualized. Rapid and robust adhesion of Tck and superantigen-activated T cells to FLS was observed that resulted in flattening of the T cells and a crawling movement on the FLS surface. Tck also readily activated FLS to produce interleukin IL-6 and IL-8 in a cell contact-dependent manner that was enhanced by exogenous IL-17. Although LFA-1 and ICAM-1 co-localized at the Tck-FLS synapse, blocking the LFA-1/ICAM-1 interaction did not substantially inhibit Tck effector function. However, antibody blocking of membrane tumor necrosis factor (TNF)-alpha on the Tck surface did inhibit FLS cytokine production, thus illustrating a novel mechanism for involvement of TNF-alpha in cell-cell interactions in RA synovium and for the effectiveness of TNF-alpha blockade in the treatment of RA.

Recruitment of phosphorylated small heat shock protein Hsp27 to nuclear speckles without stress

During stress, the mammalian small heat shock protein Hsp27 enters cell nuclei. The present study examines the requirements for entry of Hsp27 into nuclei of normal rat kidney (NRK) renal epithelial cells, and for its interactions with specific nuclear structures. We find that phosphorylation of Hsp27 is necessary for the efficient entry into nuclei during heat shock but not sufficient for efficient nuclear entry under control conditions. We further report that Hsp27 is recruited to an RNAse sensitive fraction of SC35 positive nuclear speckles, but not other intranuclear structures, in response to heat shock. Intriguingly, Hsp27 phosphorylation, in the absence of stress, is sufficient for recruitment to speckles found in post-anaphase stage mitotic cells. Additionally, pseudophosphorylated Hsp27 fused to a nuclear localization peptide (NLS) is recruited to nuclear speckles in unstressed interphase cells, but wildtype and nonphosphorylatable Hsp27 NLS fusion proteins are not. The expression of NLS-Hsp27 mutants does not enhance colony forming abilities of cells subjected to severe heat shock, but does regulate nuclear speckle morphology. These data demonstrate that phosphorylation, but not stress, mediates Hsp27 recruitment to an RNAse soluble fraction of nuclear speckles and support a site-specific role for Hsp27 within the nucleus.

Developmentally regulated gene expression of the small heat shock protein Hsp27 in zebrafish embryos

Mammalian small heat shock proteins including Hsp27 and alpha-B crystallin are constitutively expressed in various adult and embryonic tissues including skeletal and cardiac muscle. However, the function of these proteins during embryonic development is not understood, and information on their expression during the earliest stages of development is limited. We have recently demonstrated constitutive and stress inducible expression of a homologue of human Hsp27 in adult zebrafish, an important experimental model of vertebrate developmental processes. Here, we assessed the temporospatial dynamics of zebrafish Hsp27 (hsp27) and alpha-B crystallin (cryab) gene expression using reverse-transcriptase PCR (RT-PCR) and hsp27 expression by in situ hybridization. Our results reveal that initial upregulation of hsp27 expression occurs during early gastrulation. Expression of hsp27 is detected transiently in developing myotomes, lens and brain, and more persistently in developing heart. The constitutive expression level of hsp27 in embryos at some stages of development is considerably greater than that observed in unstressed adult tissues. Expression of hsp27 was also observed in all tissues examined in embryos recovering from heat stress. The pattern of expression observed for hsp27 overlaps partially, but not completely, with that reported for other heat shock proteins.

p38 MAPK/HSP25 signaling mediates cadmium-induced contraction of mesangial cells and renal glomeruli

The environmental pollutant cadmium affects human health, with the kidney being a primary target. In addition to proximal tubules, glomeruli and their contractile mesangial cells have also been identified as targets of cadmium nephrotoxicity. Glomerular contraction is thought to contribute to reduced glomerular filtration, a characteristic of cadmium nephrotoxicity. Because p38 MAPK/HSP25 signaling has been implicated in smooth muscle contraction, we examined its role in cadmium-induced contraction of mesangial cells. We report that exposure of mesangial cells to cadmium resulted in 1) cell contraction, 2) activation of MAP kinases, 3) increased HSP25 phosphorylation coincident with p38 MAP kinase activation, 4) sequential phosphorylation of the two phosphorylation sites of mouse HSP25 with Ser15 being phosphorylated before Ser86, 5) reduction of oligomeric size of HSP25, and 6) association of HSP25 with microfilaments. Exposure of isolated rat glomeruli to cadmium also resulted in contraction and increased HSP25 phosphorylation. The cadmium-induced responses were inhibited by the specific p38 MAP kinase inhibitor SB-203580, and cadmium-induced phosphorylation of HSP25 was inhibited by expression of a dominant-negative p38 MAP kinase mutant. These findings tentatively suggest that cadmium-induced nephrotoxicity results, in part, from glomerular contraction due to p38 MAP kinase/HSP25 signaling-dependent contraction of mesangial cells. With regard to the cellular action of HSP25, these data support a change in paradigm: in addition to its well-established cytoprotective function, HSP25 may also be involved in processes that ultimately lead to adverse effects, as is observed in the response of mesangial cells to cadmium.

Cloning, characterization, and heat stress-induced redistribution of a protein homologous to human hsp27 in the zebrafish Danio rerio

Hsp27 is a small heat shock protein (shsp) regulating stress tolerance and increasingly thought to play roles in tissue homeostasis and differentiation. The zebrafish Danio rerio is an important model for the study of developmental processes, but little is known regarding shsps in this animal. Here, we report the sequence, expression, regulation, and function of a zebrafish protein (zfHsp27) homologous to human Hsp27. zfHsp27 contains three conserved phosphorylatable serines and a cysteine important for regulation of apoptosis, but it lacks much of a C-terminal tail domain and shows low homology in two putative actin interacting domains that are features of mammalian Hsp27. zfHsp27 mRNA is most abundant in adult skeletal muscle and heart and is upregulated during early embryogenesis. zfHsp27 expressed in mammalian fibroblasts was phosphorylated in response to heat stress and anisomycin, and this phosphorylation was prevented by treatment with SB202190, an inhibitor of p38 MAPK. Expression of zfHsp27 and human Hsp27 in mammalian fibroblasts promoted a similar degree of tolerance to heat stress. zfHsp27 fusion proteins entered the nucleus and associated with the cytoskeleton of heat stressed cells in vitro and in zebrafish embryos. These results reveal conservation in regulation and function of mammalian and teleost Hsp27 proteins and define zebrafish as a new model for the study of Hsp27 function.

Sodium Arsenite Exposure Alters Cell Migration, Focal Adhesion Localization and Decreases Tyrosine Phosphorylation of Focal Adhesion Kinase in H9C2 Myoblasts

Exposure to the environmental toxicant arsenic is reported to produce a variety of effects including disruption of signal transduction pathways, cell proliferation, and apoptosis. This suggests that arsenite may not have specific targets but rather extremely broad effects. The present study was designed to test the hypothesis that arsenite alters signaling involved in focal adhesion structure and function in cultured myoblasts. H9C2 cells were exposed to 1, 2.5, 5, or 10 microM sodium arsenite for 48 h. MTT metabolism and staining by neutral red, trypan blue, and propidium iodide showed that sodium arsenite treatments of 5 microM or less were not overtly cytotoxic. At these doses, sodium arsenite did not affect the amount of polymerized actin in cells, rate of protein synthesis, or amounts of vinculin, talin, paxillin, and focal adhesion kinase (FAK) in cells. However, sodium arsenite-treated cells contained fewer focal adhesions with an altered distribution pattern. Sodium arsenite exposure caused a dose-dependent reduction in cell migration and cell attachment rates. The average area of substrate covered by a cell was also reduced, although the average volume of cells was not significantly affected. Sodium arsenite exposure resulted in reduced tyrosine phosphorylation of FAK, its substrate paxillin and the FAK auto- phosphorylation site, Tyr397. Our results indicate that sodium arsenite can alter focal adhesion structure and function, thus affecting cell attachment and migration and possibly other aspects of focal adhesion function such as integrin signaling. These diverse consequences may be mediated by a relatively specific inhibition of FAK tyrosine phosphorylation, modifying scaffolding proteins.

HSP27 regulates fibroblast adhesion, motility, and matrix contraction

Heat shock protein 27 (HSP27) modulates actin-dependent cell functions in several systems. We hypothesized that HSP27 modulates wound contraction. Stably transfected fibroblast cell lines that overexpress HSP27 (SS12) or underexpress HSP27 (AS10) were established, and cell behaviors related to wound contraction were examined. First, fibroblast-populated collagen lattice (FPCL) contraction was examined because it has been studied as a wound-healing model. In floating FPCL contraction assays, SS12 cells caused increased contraction, whereas AS10 cells caused reduced contraction. Because floating matrix contraction is thought to be mediated by the tractional force of the cells, cell behaviors related to tractional force were examined. In collagen matrix, SS12 cells elongated faster and to a greater extent and contained longer stress fibers than control cells, whereas AS10 cells were slower to elongate than control cells. SS12 cells attached to the dishes more efficiently than the control, whereas AS10 cells attached less efficiently. Migration of SS12 cells on collagen-coated dishes was also enhanced, although AS10 cells did not differ from the control cells. In summary, HSP27 regulates fibroblast adhesion, elongation, and migration and the contraction of the floating matrix in a manner dependent on the level of its expression.

Interaction of Human HSP22 (HSPB8) with Other Small Heat Shock Proteins

Mammalian small heat shock proteins (sHSP) are abundant in muscles and are implicated in both muscle function and myopathies. Recently a new sHSP, HSP22 (HSPB8, H11), was identified in the human heart by its interaction with HSP27 (HSPB1). Using phylogenetic analysis we show that HSP22 is a true member of the sHSP superfamily. sHSPs interact with each other and form homo- and hetero-oligomeric complexes. The function of these complexes is poorly understood. Using gel filtration HPLC, the yeast two-hybrid method, immunoprecipitation, cross-linking, and fluorescence resonance energy transfer microscopy, we report that (i). HSP22 forms high molecular mass complexes in the heart, (ii). HSP22 interacts with itself, cvHSP (HSPB7), MKBP (HSPB2) and HSP27, and (iii). HSP22 has two binding domains (N- and C-terminal) that are specific for different binding partners. HSP22 homo-dimers are formed through N-N and N-C interactions, and HSP22-cvHSP hetero-dimers through C-C interaction. HSP22-MKBP and HSP22-HSP27 hetero-dimers involve the N and C termini of HSP22 and HSP27, respectively, but appear to require full-length protein as a binding partner.

Hsp27, Hsp70, and metallothionein in MDCK and LLC-PK1 renal epithelial cells: effects of prolonged exposure to cadmium

Cadmium is a widely distributed industrial and environmental toxin. The principal target organ of chronic sublethal cadmium exposure is the kidney. In renal epithelial cells, acute high-dose cadmium exposure induces differential expression of proteins, including heat shock proteins. However, few studies have examined heat shock protein expression in cells after prolonged exposure to cadmium at sublethal concentrations. Here, we assayed total cell protein, neutral red uptake, cell death, and levels of metallothionein and heat shock proteins Hsp27 and inducible Hsp70 in cultures of MDCK and LLC-PK1 renal epithelial cells treated with cadmium for 3 days. Treatment with cadmium at concentrations equal to or greater than 10 microM (LLC-PK1) or 25 microM (MDCK) reduced measures of cell vitality and induced cell death. However, a concentration-dependent increase in Hsp27 was detected in both cell types treated with as little as 5 microM cadmium. Accumulation of Hsp70 was correlated only with cadmium treatment at concentrations also causing cell death. Metallothionein was maximally detected in cells treated with cadmium at concentrations that did not reduce cell vitality, and further increases were not detected at greater concentrations. These results reveal that heat shock proteins accumulate in renal epithelial cells during prolonged cadmium exposure, that cadmium induces differential expression of heat shock protein in epithelial cells, and that protein expression patterns in epithelial cells are specific to the cadmium concentration and degree of cellular injury. A potential role for Hsp27 in the cellular response to sublethal cadmium-induced injury is also implicated by our results.

The apoptotic ligands TRAIL, TWEAK, and Fas ligand mediate monocyte death induced by autologous lupus T cells

Individuals with systemic lupus erythematosus show evidence of a significant increase in monocyte apoptosis. This process is mediated, at least in part, by an autoreactive T cell subset that kills autologous monocytes in the absence of nominal Ag. We have investigated the apoptotic pathways involved in this T cell-mediated process. Expression of the apoptotic ligands TRAIL, TNF-like weak inducer of apoptosis (TWEAK), and Fas ligand on lupus T cells was determined, and the role of these molecules in the monocyte apoptotic response was examined. We report that these apoptotic ligands mediate the autologous monocyte death induced by lupus T cells and that this cytotoxicity is associated with increased expression of these molecules on activated T cells, rather than with an increased susceptibility of lupus monocytes to apoptosis induced by these ligands. These results define novel mechanisms that contribute to increased monocyte apoptosis characterizing patients with lupus. We propose that this mechanism could provide a source of potentially antigenic material for the autoimmune response and interfere with normal clearing mechanisms.

Site-specific alteration of actin assembly visualized in living renal epithelial cells during ATP depletion

Disruption of normal actin organization in renal tubular epithelial cells is an important element of renal injury induced by ischemia. Studies of fixed cells indicate that the cytoskeleton is disrupted by both ischemia and ATP depletion in a site-specific manner. However, few studies have examined these effects in living cells, and the relationship between the time course of ATP reduction and alteration of the cytoskeleton remains unclear. Here, time-lapse video images of cultured renal epithelial cells expressing an enhanced green fluorescent protein (EGFP)-actin fusion protein were obtained, and the kinetics of fluorescence actin distribution before and during ATP depletion is quantified and compared with measured ATP levels. This study found that assembly of lamellar actin is inhibited rapidly as cellular ATP levels are reduced, whereas disruption of actin in stress fibers is more gradual and persistent. Actin associated with focal adhesions is largely resistant to ATP depletion in these experiments, and, consistent with previous studies, particulate aggregates of actin were formed within the cytoplasm of ATP-depleted cells. Most surprisingly, time-lapse imaging of EGFP-actin distribution, quantitative fluorescence imaging of phalloidin-stained cells, and ultrastructural studies indicate that assembly of actin filaments occurs at sites of epithelial cell-cell attachment in ATP-depleted cells. This assembly is initiated early during ATP depletion and continues after ATP levels are maximally reduced. Assembly of actin at sites of cell-cell attachment may be an element of the pathology of injury induced by ischemia, or alternatively, could reflect the function of a protective mechanism. These studies directly demonstrate site-specific alteration of actin assembly in living epithelial cells during ATP depletion. The results also reveal that actin reorganization continues after ATP levels are maximally decreased and that epithelial cell-cell attachments are sites of actin assembly in ATP-depleted cells.

Heat shock protein 27 associates with basolateral cell boundaries in heat-shocked and ATP-depleted epithelial cells

Heat stress alters epithelial barrier function, and heat stress preconditioning protects epithelial function from injury. Hsp27 is a small stress protein that has previously been shown to modulate actin assembly. Thus, by regulating actin filaments associated with cell junctions, hsp27 could alter epithelial function. To begin to address this hypothesis, the regulation and distribution of a human hsp27-green fluorescence fusion protein ((EGFP)hHsp27) that is expressed in cultured renal epithelial cells was assessed. (EGFP)hHsp27, like the endogenous hsp27, associated with the cytoskeleton in heat-stressed and chemically ATP-depleted cells, and both proteins were regulated similarly. Confocal microscopy of intact and detergent-lysed cells revealed novel distribution patterns in which (EGFP)hHsp27 associated with basolateral, but not apical, cell borders in injured cells. Double labeling studies revealed (EGFP)hHsp27 and actin filament colocalization in ATP-depleted cells. However, during heat shock, granules of (EGFP)hHsp27 were found at sites of cell-cell contact and in the cell body, but colocalization with actin was not apparent. Thus, heat stress and ATP depletion induce distinct patterns of hsp27 redistribution in epithelial cells, and sites of cell-cell and cell-substrate attachment are unique in their ability to recruit hsp27 during injury. The association of (EGFP)hHsp27 with basolateral cell boundaries supports a potential role for hsp27 in protection or regulation of epithelial cell-cell and cell-substrate attachments.

Dendritic cells genetically engineered to express IL-4 inhibit murine collagen-induced arthritis

Dendritic cells (DCs) are specialized antigen-presenting cells that migrate from the periphery to lymphoid tissues, where they activate and regulate T cells. Genetic modification of DCs to express immunoregulatory molecules would provide a new immunotherapeutic strategy for autoimmune and other diseases. We have engineered bone marrow-derived DCs that express IL-4 and tested the ability of these cells to control murine collagen-induced arthritis (CIA), a model for rheumatoid arthritis in which Th1 cells play a critical role. IL-4-transduced DCs inhibited Th1 responses to collagen type II in vitro. A single injection of IL-4-transduced DCs reduced the incidence and severity of CIA and suppressed established Th1 responses and associated humoral responses, despite only transient persistence of injected DCs in the spleen. In contrast, control DCs and IL-4-transduced T cells or fibroblastic cells failed to alter the course of the disease. The functional effects correlated well with the differential efficiency of DC migration from various sites of injection to lymphoid organs, especially the spleen. The ability of splenic T cells to produce IL-4 in response to anti-CD3 was enhanced after the administration of IL-4-transduced DCS: These results support the feasibility of using genetically modified DCs for the treatment of autoimmune disease.

Restriction of secretory granule motion near the plasma membrane of chromaffin cells

We used total internal reflection fluorescence microscopy to study quantitatively the motion and distribution of secretory granules near the plasma membrane (PM) of living bovine chromaffin cells. Within the approximately 300-nm region measurably illuminated by the evanescent field resulting from total internal reflection, granules are preferentially concentrated close to the PM. Granule motion normal to the substrate (the z direction) is much slower than would be expected from free Brownian motion, is strongly restricted over tens of nanometer distances, and tends to reverse directions within 0.5 s. The z-direction diffusion coefficients of granules decrease continuously by two orders of magnitude within less than a granule diameter of the PM as granules approach the PM. These analyses suggest that a system of tethers or a heterogeneous matrix severely limits granule motion in the immediate vicinity of the PM. Transient expression of the light chains of tetanus toxin and botulinum toxin A did not disrupt the restricted motion of granules near the PM, indicating that SNARE proteins SNAP-25 and VAMP are not necessary for the decreased mobility. However, the lack of functional SNAREs on the plasma or granule membranes in such cells reduces the time that some granules spend immediately adjacent to the PM.

Automated difference image analysis of lamellar ruffling: effect of temperature change on human SH-SY5Y neuroblastoma cells

Quantitation of cell movement and lamellar extension is critical to the study of growth factors, chemotactic agents and signaling cascades. Many studies are conducted by examining the size or number of lamellae in static images of cells. However, these methods do not quantify lamellar behavior over time and may overlook important changes in lamellar function. Most presently available methods for analyzing dynamic aspects of lamellar function examine changes in a cell's 2-dimensional perimeter and are best suited to the analysis of flattened lamellae. However, some cells generate 3-dimensional lamellar ruffles whose behavior is not readily detected using these methods. In the present study we analyze temperature-dependent ruffling of human SH-SY5Y neuroblastoma cells using automated digital subtraction of time-lapse images and quantitation of the resultant 'difference' image, and compare results obtained using this and other approaches. We report that ruffling behavior of SH-SY5Y cells is measurably altered by temperature changes of as little as 1 degrees C, and that these changes are best detected using difference image analysis. Our studies indicate that temperature is a critical variable in studies of SH-SY5Y behavior and that difference image analyses may be an important complement to other methods in the study of lamellar ruffling.

Formation of F-actin aggregates in cells treated with actin stabilizing drugs

We have electroporated Dictyostelium amoebae with fluorescent phalloidin in order to visualize the localization and behavior of F-actin filaments in living cells. Immediately after electroporation with phalloidin, cells became round and showed bright staining in the cortical region. Over time, the cortical staining disappeared and was replaced by a large aggregate of actin filaments. The aggregates were predominantly localized to the apical posterior of actively moving cells and in the middle of dividing cells or stationary AX4 cells. Mutants lacking myosin II or ABP-120 also formed actin aggregates; however, the rate of formation of aggregates was slower in myosin II mutant cells. In order to investigate this phenomenon further, we have used jasplakinolide, a membrane-permeable drug that also stabilizes F-actin filaments. Cells treated with jasplakinolide formed actin aggregates in a concentration-dependent manner. Drug treatment led to an increase in the proportion of actin associated with the cytoskeleton. Jasplakinolide-treated cells were still motile; however, their rate of movement was less than that of untreated cells. Cytochalasin B and nocodazole had inhibitory effects on aggregate formation, while azide blocked the process completely. We hypothesize that aggregates are formed from the cortical flow of F-actin filaments. These filaments would normally be depolymerized but are artificially stabilized by phalloidin or jasplakinolide binding. The localization of the aggregate is likely to be an indication of the direction of cortical flow.

Changes in actin filament organization during pseudopod formation

Fluorescent phalloidin has been introduced into Dicytostelium amoebae in order to visualize dynamic changes in the localization of F-actin during pseudopod extension. Phalloidin was initially localized to the peripheral cortex of the cell. Newly formed pseudopods were not fluorescent, indicating that phalloidin was tightly bound to existing F-actin filaments and could not rapidly relocalize to newly formed filaments. As pseudopod extension proceeded, the fluorescent signal disappeared from the region directly underlying the expansion zone, leaving a gap in the actin cortex. Similar results were obtained in both wild-type cells and those lacking myosin II heavy chain. The disappearance of the fluorescent signal from the cortical region underlying the new pseudopod is presumed to be due to breakdown of the actin cortex and dispersion of the remnants. These results suggest that new pseudopods are not built upon the existing actin cortex but rather that the cortex is locally solated as part of the construction of the new actin network.

Tyrosine phosphorylation of paxillin and focal adhesion kinase during insulin-like growth factor-I-stimulated lamellipodial advance

In the current studies, we examined whether focal adhesion kinase (FAK) and paxillin play a role in insulin-like growth factor-I (IGF-I)-stimulated morphological changes in neuronal cells. In SH-SY5Y human neuroblastoma cells, 10 nM IGF-I enhanced the extension of lamellipodia within 30 min. Scanning electron microscopy and staining with rhodamine-phalloidin showed that these lamellipodia displayed ruffles, filopodia, and a distinct meshwork of actin filaments. Immunofluorescent staining identified focal concentrations of FAK, paxillin, and phosphotyrosine within the lamellipodia. Immunoprecipitation experiments revealed that FAK and paxillin are tyrosine-phosphorylated during IGF-I-stimulated lamellipodial extension. Maximal phosphorylation of FAK and paxillin was observed 15-30 min after the addition of 10 nM IGF-I, whereas maximal IGF-I receptor phosphorylation occurred within 5 min. FAK, paxillin, and IGF-I receptor tyrosine phosphorylation had similar concentration-response curves and were inhibited by the receptor blocking antibody alphaIR-3. These results indicate that FAK and paxillin are tyrosine-phosphorylated during IGF-I-stimulated lamellipodial advance and suggest that the tyrosine phosphorylation of these two proteins helps mediate IGF-I-stimulated cell and growth cone motility. These responses contrast directly with recent reports showing insulin-stimulated dephosphorylation of FAK and paxillin.